Stent-graft assembly with thin-walled graft component and method of manufacture

ABSTRACT

A stent-graft assembly having a thin-walled membrane and method of preparing the same are disclosed. In a first embodiment, the assembly comprises a stent, a coating and a porous membrane, wherein the membrane is less than 0.040 inch thick or less. Portions of the coating extend into the pores of the thin membrane to sealingly engage the membrane to achieve secure adhesion. In a second embodiment the coating and thin membrane bond to form a homogenous structure. In an alternative embodiment, the assembly comprises an inner and outer thin membrane bound to one another through the interstices of the support member and a coating at the proximal and distal regions. In any of the foregoing embodiments, the proximal and distal regions of the stent-graft assembly may comprise an additional coating, whereby layers of material are sealed, thereby minimizing thrombogenic potential of free ends of the assembly.

FIELD OF THE INVENTION

[0001] The present invention relates generally to endoluminal grafts forstenotic or diseased lumens and methods of making such grafts. Moreparticularly, the invention includes a stent-graft assembly comprising athin-walled graft component and methods of making the assembly.

BACKGROUND OF THE INVENTION

[0002] A wide range of medical treatments have been previously developedusing “endoluminal prostheses,” which terms are herein intended to meanmedical devices which are adapted for temporary or permanentimplantation within a body lumen, including both naturally occurring orartificially made lumens. Examples of lumens in which endoluminalprostheses may be implanted include, without limitation: arteries, suchas those located within the coronary, mesentery, peripheral, or cerebralvasculature; veins; gastrointestinal tract; biliary tract; urethra;trachea; hepatic shunts; and fallopian tubes. Various types ofendoluminal prostheses have also been developed, each providing auniquely beneficial structure to modify the mechanics of the targetedluminal wall.

[0003] For example, various grafts, stents, and combination stent-graftprostheses have been previously disclosed for implantation within bodylumens. More specifically regarding stents, various designs of theseprostheses have been previously disclosed for providing artificialradial support to the wall tissue which forms the various lumens withinthe body, and often more specifically within the blood vessels of thebody. An example of such a stent displaying optimal radial strengthincludes, but is not limited to, the stent disclosed in U.S. Pat. No.5,292,331 to Boneau, the disclosure of which is herein incorporated byreference. Stents of other designs are known in the art, and may also besuitable for use in the stent-graft assembly. Other example of stentsinclude but are not limited to those disclosed in U.S. Pat. No.4,733,665 issued to Palmaz, U.S. Pat. No. 5,195,984 issued to Schatz, orU.S. Pat. No. 5,514,154 issued to Lau. Stents are used alone or inconjunction with grafts.

[0004] The use of an angioplasty balloon catheter is common in the artas a minimally invasive treatment to enlarge a stenotic or diseasedblood vessel. This treatment is known as percutaneous transluminalangioplasty, or PTA. To provide radial support to the treated vessel inorder to prolong the positive effects of PTA, a stent may be implantedin conjunction with the procedure. Under this procedure, the stent maybe collapsed to an insertion diameter and inserted into a body lumen ata site remote from the diseased vessel. The stent may then be deliveredto the desired site of treatment within the affected lumen and deployedto its desired diameter for treatment. Although the stents listed aboveare balloon expandable, stents which rely on other modes of deploymentsuch as self-expansion, may be used to make a device according to thepresent invention. Because the procedure requires insertion of the stentat a site remote from the site of treatment, the device must be guidedthrough the potentially tortuous conduit of the body lumen to thetreatment site. Therefore, the stent must be capable of being reduced toa small insertion diameter and must be flexible.

[0005] During an angioplasty procedure, atheromatous plaques undergofissuring, thereby creating a thrombogenic environment in the lumen.Excessive scarring may also occur following the procedure, potentiallyresulting in reocclusion of the treated lumen. Attempts to address theseproblems include providing a suitable surface within the lumen for morecontrolled healing to occur in addition to the support provided by astent. These attempts include providing a lining or covering inconjunction with an implanted stent. A stent with such a lining orcovering is known in the art as a stent-graft.

[0006] The graft component, or membrane, of a stent-graft may preventexcessive tissue prolapse or protrusion of tissue growth through theinterstices of the stent while allowing limited tissue in-growth tooccur to enhance the implantation. The surface of the graft material atthe same time may minimize thrombosis, prevent scarring from occludingthe lumen, prevent embolic events and minimize the contact between thefissured plaque and the hematological elements in the bloodstream.

[0007] A combination stent-graft may serve other objectives, such asdelivering therapeutic agents via the assembly, excluding aneurysms orother malformations, occluding a side branch of a lumen withoutsacrificing perforator branches, conferring radiopacity on the device,and others. Various designs to achieve these objectives include stentspartially or completely coated or covered with materials, some of whichare impregnated with therapeutic agents, radiopaque elements, or otherfeatures designed to achieve the particular objectives of the device.

[0008] A graft component may be combined with a stent in order toachieve some or all of the foregoing objectives. However, adding a graftlayer to the stent increases the challenges of delivering a stent via acatheter by increasing the crossing profile, or diameter, of the device,and by decreasing the flexibility of the device. Because the angioplastyprocess requires the insertion of the device into a body lumen at a siteremote from the site of treatment and the guiding of the device the bodylumen to the treatment site, it is required that the device be bothcapable of being collapsed to a relatively small diameter and be quiteflexible. Moreover, flexibility and a desirable insertion diameter mustbe achieved without sacrificing the treatment objectives of theassembly, which include, at a minimum, radial strength. Therefore, anobjective of a combination stent and graft is achieving the advantagesof both a stent and a graft without significantly increasing thecrossing profile of the device or significantly decreasing theflexibility of the device.

[0009] Various methods of manufacturing graft devices alone have beendisclosed in the art. One such method for manufacturing a graft isdisclosed in U.S. Pat. No. 5,641,373, issued to Shannon et al. Thedisclosed method comprises reinforcing an extruded flouropolymer tubewith a second flouropolymer tube. The second tube is prepared by windingfluoropolymer tape around the exterior of a mandrel and heating it toform a tube. The graft may then be mounted on an anchoring mechanismsuch as a stent or other fixation device.

[0010] Another example of a graft is disclosed in U.S. Pat. No.4,731,073, issued to Robinson. The graft disclosed therein comprisesmultiple layers of segmented polyether-polyurethane which form multiplezones having varying porosities.

[0011] U.S. Pat. No. 5,628,786, issued to Banas, discloses apolytetrafluoroethylene (PTFE) graft which has a reinforcing structureintegrally bound to the graft. The reinforcing structure may be in theform of a rib which is sintered or otherwise integrally bound to thegraft.

[0012] U.S. Pat. No. 5,207,960, issued to Moret de Rocheprise, disclosesa process for the manufacture of a thin-walled tube of fluorinated resintape. The method includes winding the tape around a mandrel andsintering the tape. While still on the mandrel, the tube is rolled toelongate the tube, to reduce the thickness of the tube, and tofacilitate removal of the tube from the mandrel. The patent disclosesthat the tubes obtained can be used particularly as sheaths for thelining of metal tubes.

[0013] There are also numerous examples of combination stent-graftsdisclosed in the art. U.S. Pat. No. 5,653,747 issued to Dereumediscloses a stent to which a graft is attached. The graft component isproduced by extruding polymer in solution into fibers from a spinneretteonto a rotating mandrel. A stent may be placed over the fibers while onthe mandrel and then an additional layer of fibers spun onto the stent.The layer or layers of fibers may be bonded to the stent and/or oneanother by heat or by adhesives.

[0014] PCT Application WO 95/05132 discloses a stent around which a thinfilm of PTFE has been wrapped circumferentially one time and overlappedupon itself to form a seam. The stent may be alternatively oradditionally placed to cover the interior of the stent. Fluorinatedethylene propylene is used as an adhesive to affix the graft to thestent.

[0015] A specific example of a coated stent is disclosed by Pinchuk inEuropean Patent Application EP 0 797 963 A2. The objectives of Pinchuk'sinvention include both increasing the hoop strength and decreasing thethrombogenic potential of a criss-crossed wire stent or a zig-zag stent.Pinchuk's application also discloses covering the coated stent in themanner disclosed in U.S. patent application No. 5,653,747 issued toDereume, discussed above.

[0016] An example of a stent and tubular graft is disclosed in U.S. Pat.No. 5,522,882 issued to Gaterud, et al. Gaterud discloses an expandablestent mounted on a balloon and a graft mounted over the stent.

[0017] U.S. Pat. No. 5,123,917 issued to Lee discusses a flexible andexpandable inner tube upon which separate ring scaffold members aremounted, and a flexible and expandable outer tube enclosing the innertube and scaffold members. The rings may be secured to the inner linerwith an adhesive layer. Alternatively, the liners may be adhered to eachother with the rings trapped between the layers. Lee discloses that theluminal surface of the device may be coated with various pharmacologicalagents.

[0018] Similarly, U.S. Pat. Nos. 5,282,823 and 5,443,496, both issued toSchwartz, et al. disclose a stent with a polymeric film extendingbetween the stent elements, and strain relief means in the form of cutsin the film to allow the stent to fully expand and conform to theinterior of the lumen. The thin polymeric film is applied to the stentwhile in solution and dried. Once dried, cuts are made in the film toprovide strain relief means.

[0019] Another assembly includes a stent embedded in a plastic sleeve orstitched or glued to a nylon sleeve, as in U.S. Pat. No. 5,507,771,issued to Gianturco. Other prior art devices requiring stitching of thegraft to the stent are disclosed in European Patent Application EP 0 686379 A2, which teaches a perforate tubular frame having a fabric linerstitched to the frame, and World Intellectual Property OrganizationApplication Number WO 96/21404 which indicates that the graft bestitched to the stent, and possibly to loops or eyelets which are partof the stent structure.

[0020] U.S. Pat. No. 5,637,113 issued to Tartaglia teaches a stent witha sheet of polymeric film wrapped around the exterior. Tartaglia teachesthat the film is attached to the stent at one end by an adhesive, by ahook and notch arrangement, or by dry heat sealing. The polymer can alsobe attached to the stent by wrapping the film circumferentially aroundthe stent and attaching the polymer film to itself to form a sleevearound the stent by heating and melting the film to itself, adhesivebonding, solvent bonding, or by mechanical fastening, such as by a clip.The film may be loaded or coated with a therapeutic agent.

[0021] U.S. Pat. No. 5,628,788, issued to Pinchuk, discloses a processof melt-attaching a graft to a stent by disposing a layer of materialbetween the stent and graft which has a lower melting point than thegraft, and heating the assembly to the melting point of the low-meltingpoint material. Pinchuk also teaches adhering a textile graft to a stentby coating a stent with vulcanizing silicone rubber adhesive and curingthe adhesive. Pinchuk discloses a similar stent-graft assembly inEuropean Patent Application EP 0 689 805 A2 and teaches that the graftmember can be bonded to the stent member thermally or by the use ofadhesive agents.

[0022] Similarly, World Intellectual Property Organization ApplicationNo. WO 95/05132 discloses a stent with and inner and/or an outer linerwrapped around the stent to form a seam, with the liner(s) affixed usingan adhesive or melt-attached using a layer of a material with a lowermelting point.

[0023] U.S. Pat. No. 5,645,559, issued to Hachtman, et al., discloses amultiple layer stent-graft assembly comprising a first layer defining ahollow tubular construction, a second layer having a self-expandingbraided mesh construction and a layer of polymeric material disposedbetween the first and second layers. The polymeric material may beadhered by two-sided adhesive tape. The self-expanding braided mesh, thetubular material, or both may be larger in diameter in the distalregions than in the medial region.

[0024] U.S. Pat. No. 5,534,287, issued to Lukic, discloses methods whichresult in a covered stent, the covering adhered via a lifting medium.

[0025] U.S. Pat. No. 5,674,241, issued to Bley, et al. teaches that ahydrophilic polymer layer may be laminated, embedded, coated, extruded,incorporated, or molded around an expandable mesh stent while the stentis in its collapsed condition, and the stent and graft permitted toexpand upon hydration.

[0026] European Patent Application No. EP 0 775 472 A2 discloses aPTFE-covered stent. The stent can be covered by diagonally winding anexpanded PTFE tape under tension around an at least partially expandedstent.

[0027] Challenges arising in the art which none of the prior artadequately addresses include achieving a stent-graft assembly ofsufficiently small crossing profile and which is sufficiently flexible.Other challenges include minimizing, if not eliminating, migration ofthe stent, graft or stent-graft; minimizing, if not eliminating,delamination of the stent and graft material; and minimizingthrombogenic potential, vessel reocclusion and tissue prolapse followingdeployment. Shortcomings associated with the prior art include:assemblies with undesirably large crossing profiles; assemblies withinsufficient flexibility; inadequate adhering of coatings and coveringsto stents; inadequate adhering of coatings to coverings; failure toshield the injured vascular surface; failure to prevent tissue ingrowthfrom occluding the lumen; failure to minimize the embolization ofparticles loosely adherent to the vessel wall (especially during deviceplacement and deployment); and increased thrombogenic potential arisingfrom delamination of the stent and graft material.

SUMMARY OF THE INVENTION

[0028] The present invention and its varied embodiments address severalproblems associated with the prior art. It is a first objective of thisinvention to provide an improved stent-graft assembly for the repair andsupport of a body lumen. It is a second objective of this invention toprovide an improved stent-graft assembly with ample radial strength andminimal thrombogenic potential without appreciably increasing theprofile of the device over that of the stent alone. Further, thedecreased profile following deployment may reduce the thrombogenicpotential of the device. It is a further objective of this invention toprovide a thin-walled stent-graft with both ample radial strength andample flexibility.

[0029] It is a further objective of this invention to solve the problemin the prior art of inadequate adhesion between the stent and graftmaterial.

[0030] An additional objective of this invention is to balance the needfor some tissue in-growth against the need to minimize thrombogenicpotential and excessive cell growth through the interstices of thestent. This objective is achieved by providing a non-thrombogenic,thin-walled stent-graft assembly which is a smoother device, especiallyin regions where the prior art stent-graft has a tendency to fray,delaminate, or exhibit a scissoring effect. This objective is alsoachieved by providing a thin-walled stent-graft assembly which shieldsthe injured vascular surface, controls excessive tissue in-growththrough the stent, and minimizes the embolization of particles looselyadherent to the vessel wall especially during placement and deploymentof the device. The device can also be used to control the luminalprotrusion of dissection planes created during PTA or spontaneousfissuring.

[0031] A stent-graft assembly according to the present invention firstcomprises a generally cylindrical stent which comprises at least onesupport member. Some or all of the support member or members comprise acoating which substantially encapsulates the coated support member ormembers. Further, the stent-graft includes an ultra-thin membrane orcovering which is attached to the coating.

[0032] In one embodiment, the proximal and distal regions of thestent-graft have an additional coating over the first coating and themembrane. In an alternative embodiment, the proximal and distal regionsof the stent may be left completely uncoated and uncovered if needed forthe particular medical application of the device.

[0033] The thin membrane may be either on the inner or the outer surfaceof the stent or both. The material used for the membrane comprises anultra-thin polymer. In use, the membrane may have varying degrees ofdistensibility depending upon the desired application of the device. Themembrane is bound to the coating either as a result of defining ahomogeneous material with the coating or as a result of extensions ofthe coating into the pores of the membrane and the resultinginterlocking engagement between the coating extensions and the pores ofthe membrane to form a composite. An alternative embodiment of theinvention comprises a stent with either a continuous membrane or morethan one membrane on the interior and on the exterior of the stent, themembranes bound to one another through the interstices of the stent. Themembrane(s) may be sintered or otherwise bound to itself or to oneanother. The invention also contemplates the use of a coating at theproximal and distal regions of the stent, which substantiallyencapsulates the assembly at the proximal and distal regions.

[0034] The method according to a first embodiment of the presentinvention comprises helically wrapping ultra-thin polymeric tape arounda mandrel, adjusting the angle of orientation of the tape to the mandreldepending upon the desired distensibility of the membrane and allowingadjacent edges of the helical wrapping to overlap somewhat; sinteringthe tape to itself over the mandrel to produce a thin tube; removing thethin tube from the mandrel; coating a stent with a polymer; coveringand/or lining the coated stent with the thin tube; introducing a solventto attach the coating to the membrane; curing the assembly to drive offremaining solvent.

[0035] The method according to an alternative embodiment compriseswinding the polymeric tape around the mandrel to form two layers, ineach layer reversing the angle of orientation of the tape to thelongitudinal axis of the mandrel to form a bias ply, and then followingthe remaining steps of the method described above. In any givenembodiment, the angle of orientation of the tape to the longitudinalaxis of the mandrel, dependent on the width of tape and diameter of themandrel, can be varied depending upon the desired distensibility of thegraft component of the device. The sintering parameters can also bevaried to affect the distensibility of the device. Further, pressure maybe utilized in conjunction with sintering to improve the adherence ofthe tape. And finally, the amount of overlap between adjacent edges oftape can be varied depending upon the particular indication for thedevice.

[0036] In yet a further embodiment of a method according to theinvention, a thin-walled stent-graft assembly, having inner and outermembranes, can be fabricated utilizing pressure and heat.

[0037] In any of the methods according to the particular embodiment, theextent that the coating and membrane cover the stent can be varied. Andthe manner in which the membrane is wrapped about the mandrel,specifically, helically or otherwise. Also according to the particularembodiment, the proximal and distal regions of the stent-graft assemblymay be coated a second or multiple times to seal the resulting layers ofstent, coating and membrane, and to substantially increase bond strengthdue to the increased surface area of the encapsulation of the stentstrut.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1 illustrates a perspective view of a suitable stent for usein the present invention.

[0039]FIG. 2 illustrates a perspective view with a progressive partialcut-away of an embodiment of the stent-graft assembly according to thepresent invention.

[0040] FIGS. 3A-3C illustrate a portion of the method of preparation ofthe membrane component of an embodiment of the stent-graft assemblyaccording to the present invention.

[0041]FIGS. 4A and 4B illustrate a cross-sectional view of an embodimentof the invention taken along line A-A of FIG. 2.

[0042] FIGS. 5A-5D respectively illustrate the sequential results of thesteps of a method according to one embodiment of the present invention.

[0043]FIGS. 6A and 6B show a cross-sectional view of the device takenalong line A-A of FIG. 2 of an alternate embodiment of the presentinvention.

[0044] FIGS. 7A-7D respectively illustrate the sequential results of thesteps of a method according to one embodiment of the present invention.

[0045]FIG. 8 illustrates a perspective view of a partial progressivecut-away of an alternative embodiment of the invention.

[0046]FIG. 9 illustrates a perspective view of a partial progressivecut-away of yet another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] The thin-walled stent-graft assembly according to the presentinvention is shown in FIG. 2. One recommended stent for use as the stentmember according to the present invention is shown at stent (9) inFIG. 1. Other stents, such as those disclosed in U.S. Pat. No. 4,733,665issued to Palmaz, U.S. Pat. No. 5,195,984 issued to Schatz, or U.S. Pat.No. 5,514,154 issued to Lau may also be suitable for use in the stentgraft assembly.

[0048] Stent (9) is shown in FIG. 1 to include a series of connected,individual sinusoidal-shaped stent elements (10). Each individualelement is similar in design and construction to the endovascularsupport device disclosed in U.S. Pat. No. 5,292,331 issued to Boneau,the disclosure of which is herein incorporated by reference thereto. Forthe purpose of further illustration, however, the series of adjacentrings or circumferential wires form support members, such as is shownfor the purpose of illustration at support member (11). Each ring isformed to include a serpentine shape which includes a plurality of peaksand struts extending longitudinally between adjacent peaks, such as isshown for example at strut (12) which extends between peaks (13,14).Each ring is further connected to an adjacent ring in at least onelocation where the peaks of their serpentine shape meet, resulting in aninterconnected series of stent elements which forms generallycylindrical body (15). Cylindrical body (15) further forms a prosthesispassageway (16) extending through the plurality of adjacent,serpentine-shaped rings along longitudinal axis L and between proximalprosthesis port (17) and distal prosthesis port (18).

[0049] Further to the interconnected series of stent elements and theirrespective wire-like support members which form cylindrical body (15) asshown in FIG. 1, spaces remain along cylindrical body (15) betweenadjacent peaks of each shaped ring and also between adjacent rings,particularly where the individual peaks of adjacent rings extend awayfrom each other relative to longitudinal axis L.

[0050] Turning now to FIG. 2, a stent-graft assembly according to oneembodiment of the present invention comprises a stent (9) having acoating (20) on some or all of the support members (11). The stent-graftassembly further comprises a thin membrane (21) which in this embodimentdefines a vascular surface (22), but which in alternate embodiments mayform a luminal surface or both a vascular and luminal surface. Themembrane is less than 0.040 inch in thickness, and preferably is 0.00016inch thick or less, and is distensible over a range of between 7 and 100per cent over its primary unstretched diameter. Suitable material forthe membrane may be synthetic and is preferably expandedpolytetrafluoroethylene (ePTFE), but may include but is not limited topolyesters, polyurethane and silicone.

[0051] The proximal and distal regions may comprise a second coating(34), as illustrated on the distal region only in FIG. 2. Suitablematerial for the coating includes but is not limited to polyurethane,fluorinated ethylene propylene, and silicone. A therapeutic agent orradiopaque marker may be incorporated into the second coating or themembrane using a number of different techniques known in the art,including loading, coating or laminating.

[0052] A portion of the method of preparation of the thin-walled graftcomponent is illustrated in FIGS. 3A and 3B. Successive helical windings(70) of the thin polymeric tape (0.010 inches in thickness or less)(72)overlap to a desired extent. The amount of overlap can be varieddepending upon the width of the tape, diameter of mandrel and the angleof the tape to the longitudinal axis of the mandrel. The inventioncontemplates that the adjacent edges of the tape overlap between 5 and90 per cent of the width of the tape, with 10 to 60 per cent preferred.The finished graft component is distensible over a varying rangedepending upon the angle α of the tape to the longitudinal axis of themandrel L. The lesser the angle α, the greater the radialdistensibility. The degree of distensibility is also affected by thesintering process, and the parameters followed to achieve sintering ofthe tape may be varied depending upon the desired radial distensibility.The tape can be wound at any desired angle α to the longitudinal axis ofthe mandrel, more specifically, α≦90°. But in this embodiment the angleis preferably between 30 and 60 degrees. The tape is wound beginningfrom one end of the mandrel progressively to the other end of themandrel. It can then be wound a second time in the reverse direction ifan additional layer of polymeric tape is desired, such as shown in FIG.3C.

[0053] The wrapped mandrel is then subject to a sufficient temperaturefor a sufficient time to sinter the overlap layers together. Forexample, a PTFE wrapped mandrel is subject to a temperature ofapproximately 370 degrees C. for between 30 and 45 minutes to sinter theoverlapping portions together. Pressure may be utilized in conjunctionwith sintering to improve the adherence of the tape windings to oneanother.

[0054] An alternative sintering method for forming the thin-walled tubeutilizes a radial compression process such as, hot isostaticcompression. A preferred embodiment of which comprises placing thewrapped mandrel into a vial which is packed in a media such as, silicaor other microbeads. A plunger is placed and held within the vial underpressure. The vial containing the wrapped mandrel under pressure is thenheated at sufficient time and temperature to achieve sintering. Asillustrated in FIG. 3B, after sintering, the ends (74) of the newlyformed tube are trimmed. Moreover, with respect to the use of non-PTFEtape, rather than sintering, the tape could be solvent bonded, UV bondedor the overlapping portions could be bonded together through the use ofa pressure-sensitive adhesive.

[0055] The thin tube is then removed from the mandrel. If, because thetube constricts to some degree during sintering, difficulty isencountered in removing the tube from the mandrel, several methods tofacilitate removing the tube may be used. Compressed air may bedischarged at one end of the tube between the tube and the mandrel, or aflat tool may be used to loosen any temporary adhesion between themandrel and the tube. Alternatively, a collapsible mandrel or a bar ofreducible diameter may be used. Also, a lubricant such as silicone, canbe introduced to facilitate removal of the tube from the mandrel.

[0056] The entire stent-graft assembly can also be fabricated inaccordance with method for producing the thin-walled tube utilizingpressure and heat as discussed above. Specifically, a first tape iswrapped about the mandrel. Next, the stent is loaded onto the mandrelover the first tape. A second tape is then wrapped over the stent. Theentire assembly is then placed into a vial which is packed withmicrobeads. The assembly is then subjected to pressure and heat for asufficient time and at a sufficient temperature to achieve sintering.Additionally, rather than placing the assembly in a microbead-filledvial, the membranes of the assembly may be sintered together by placingthe assembly in an oven at approximately 370° C.

[0057] In the embodiment of the invention shown in FIGS. 4A and 4B, thematerials comprising both the coating (20) and the thin-walled membrane(21) are typically of chemically similar materials, preferablypolyurethanes, such that when the assembly is subjected to a solvent,the coating and thin-walled membrane partially dissolve. The solvent canbe introduced via a vapor deposition process. The assembly can be placedin an enclosed chamber with a super-saturated atmosphere of solvent. Atthe plurality of points at which they are in contact, the coating andthin-walled membrane dissolve together to form bonding regions in whichthe coating and thin-walled membrane become a homogeneous material. Inother words, the coating and thin-walled membrane unite to define aunitary structure (24). Although a non-porous thin-walled membrane isdepicted in FIGS. 4A through 5d, the thin-walled membrane may be porous.Suitable solvents include any solvent which will degrade, dissolve ordecrease the viscosity of the coating. Particularly suitable solventsinclude but are not limited to dimethyl acetamide, xylene, andisopropanol.

[0058] In a preferred embodiment of the invention shown in FIGS. 6Athrough 7D, the thin-walled membrane comprises a plurality of pores(32). When the assembly is subjected to an appropriate solvent, thecoating becomes decreasingly viscous. Subject to the ratio of thesolvent to the coating and the relative porosity of the thin-walledmembrane, the coating in this embodiment infiltrates the pores of thethin-walled membrane to a varying extent. A plurality of bonding regions(26) at and beyond the surface of the thin-walled membrane are formedwhere the coating fills the pores of the thin-walled membrane and, afterthe assembly is cured to drive off the solvent, sealingly engages thethin-walled membrane to the coating.

[0059] The stent is coated via either a dipping process or a sprayingprocess. In one embodiment, the spraying process is performed utilizinga 5.0% solids solution polyurethane in dimethyl acetamide. The newlycoated stent is then cured to remove solvent. The sequential results ofthe steps for attaching the coating to a non-porous graft according to afirst method of forming the thin-walled stent-graft is shownillustratively in FIGS. 5A-5D. A cross-section of the resultingstructure is illustrated in FIG. 4B. FIGS. 6A and 6B, and FIGS. 7A-7Dillustrate the results of the method when utilizing a porous materialfor the thin-walled membrane.

[0060] Further illustrating the method when utilizing a porousthin-walled membrane, following curing, the coated stent is expanded toan intermediate diameter, such as by loading it onto an expansionmandrel, and the thin polymeric tube (21) is mounted over the exteriorof the coated stent, a cross-sectional representation of which is shownin FIGS. 7B and 7C. The method could have either the alternative step orthe added step of placing a tube within the stent prior to applying thesolvent, such that the resulting assembly has a thin-walled membrane onthe interior of the stent or on both the interior and the exterior ofthe stent.

[0061] The assembly is then subjected to a solvent, such as dimethylacetamide, which will decrease the viscosity of the coating and cause itto migrate into the pores of the thin-walled membrane. The assembly isthen cured in a forced air oven to remove any remaining solvent. Theresulting bond is characterized in FIGS. 6A, 6B and 7D, showing across-section of a support member (11) encapsulated in coating, and thecoating (20) extending into the pores of the graft member or thin-walledmembrane (21) such that the coating and thin-walled membrane are ininterlocking engagement with one another. Following the removal ofsolvent, the device is configured to its insertion diameter.

[0062]FIG. 8 represents a partial progressive cut-away of anotherembodiment of the invention. In the embodiment illustrated in FIG. 8,the assembly comprises a stent (60), a first thin membrane (62) defininga lumenal surface, a second thin membrane (64) defining a vascularsurface and a coating (65). Because FIG. 8 is a progressive cut-awayillustration, the coating is illustrated as substantially encapsulatingthe distal region (68) of the assembly only, but in actualityencapsulates both the proximal and the distal regions. The thin-walledmembranes may be sintered or otherwise bonded to one another through theinterstices of the stent. The coating is bonded to the thin-walledmembranes in the same manner as in the previous embodiments.

[0063]FIG. 9 illustrates yet another embodiment of the invention, as aperspective view of a progressive partial cut-away of this additionalembodiment. In the embodiment depicted in FIG. 9, the stent (9)comprises a coating (20) substantially covering all of the supportmember or members (11). The device further comprises a thin membrane(21) which in this embodiment defines a vascular surface (22). The thinmembrane (21) is sized such that it covers the coated stent up to thelast stent element (10) on each end of the stent (9), as shown in FIG.9. Although, the membrane may alternatively extend up to and cover atleast a portion of the last stent element. The device further comprisesa second coating (34) which covers the last stent element (10) and atleast a portion of the second to last stent element at both the proximaland distal regions of the assembly, although illustrated only at thedistal region in FIG. 9.

EXAMPLE 1

[0064] For the purpose of further illustration, an exemplary method forpreparing a thin-walled stent-graft assembly is described as follows. Athin tape of ePTFE, approximately 0.0004 inch in thickness, was woundaround a 3.25 mm mandrel under slight tension at approximately a 60degree angle to the longitudinal axis of the mandrel. Adjacent edges ofthe tape overlapped approximately 67 per cent of the tape's width. Thewrapped mandrel was sintered at 370 degrees Celsius for 45 minutes.

[0065] A GFX stent, which is manufactured by Arterial VascularEngineering, Inc., in Santa Rosa, Calif., was provided in a 18 mmlength. The end of the stent was mounted on a 0.109 inch diametermandrel. The stent was pre-heated at 80 degrees Celsius. The stent wasthen sprayed at a rate of 6.3 microliters per second for 10 seconds witha 5.0% solids solution of polyurethane in dimethyl acetamide. The coatedstent was then cured for 90 seconds at 100 degrees Celsius. Theprocedure was repeated with the opposite end of the stent mounted on themandrel.

[0066] Polyurethanes which may be used in accordance with the presentinvention include segmented polycarbonate polyurethane such as that soldunder the trademark CHRONOFLEX type AR, which is available fromCardiotech, Inc., located in Woburn, Mass.

[0067] The thin ePTFE tube was removed from the mandrel and placed overthe coated stent. The stent was then expanded to a 3.5 mm diameter overan expansion mandrel while inside the thin tube previously prepared,such that the stent was well opposed to the graft wall. The stent andgraft combination were then placed in a super-saturated atmosphere ofdimethyl acetamide within an enclosed chamber. The device was then curedin a forced air oven at 80 degrees C. for fifteen minutes. Followingcuring, the ends of the stent-graft were trimmed to remove graftmaterial from between the peaks of the support members. The stent wasthen configured to its insertion diameter. Utilizing a fine-tippedsyringe dispenser, a small drop of 5% polyurethane solution was placedon each stent peak to fully encapsulate the stent member at the peak.The assembly was again cured for thirty minutes at 80 degrees Celsius.

EXAMPLE 2

[0068] Utilizing a thin, expanded polytetrafluoroethylene tape ofapproximately 0.0004 inch in thickness, the tape was wound helicallyaround a mandrel from one end of the mandrel and progressing to theother end under slight tension at an angle of approximately 50 degreesto the longitudinal axis of the mandrel. The tape was wound a secondtime in the opposite direction to form a second layer, again at an angleof approximately 50 degrees to the longitudinal axis of the mandrel.Throughout each step of wrapping the tape, adjacent edges of the tapeoverlapped approximately 30 per cent. The wrapped mandrel was thensintered at a temperature of 370 degrees Celsius for forty-five minutes.

[0069] A GFX coronary bypass stent, which is manufactured by ArterialVascular Engineering, Inc., was spray coated with five microliters persecond for five seconds with segmented polycarbonate polyurethane. Theprocess was performed with the end of the stent mounted on a mandrel,repeated an additional five times, each time alternating the end of thestent which was exposed to the spray. Between each coat, the stent wascured for five minutes in a forced air oven at 80 degrees C. The coatedstent was then cured in a forced air oven at 80 degrees Celsius for onehour, and allowed to cool.

[0070] The thin ePTFE tube was removed from the mandrel and placed overthe coated stent. The coated stent was then expanded within the preparedthin ePTFE tube on an expansion mandrel to 4.5 mm. The coated stent withgraft were then exposed to dimethyl acetamide solvent via an atomizingspray for one second at a rate 100 microliters per second at 10 secondintervals within an enclosed chamber at ambient temperature for 30minutes.

[0071] The assembly was then cured at 80 degrees Celsius in a forced airoven for 30 minutes. Following curing, the ends of the stent-graft weretrimmed to remove graft material from between the peaks of the supportmembers. The stent was then configured to its insertion diameter.

[0072] A stent-graft assembly having a thin-walled membrane and methodof manufacturing the same have been disclosed. Although the presentinvention has been described in accordance with the embodiments shown,one of ordinary skill in the art will readily recognize that there couldbe variations to the embodiments and those variations would be withinthe spirit and scope of the present invention.

[0073] A wide variety of suitable materials used for stents and graftsmay be interchanged without diverging from the methods or structures ofthe invention claimed. For example, the type of stent utilized could bevaried greatly. The embodiments disclosed herein focus on a stentcomprising independent support members, but a stent which is comprisedof a slotted tube or of a rolled film configuration may also be used.Further, suitable stents include stents made of nitinol or other shapememory alloy. In order to confer radiopacity on an alternative stent,various methods may be utilized. For example, a radiopaque metal markersuch as Gold, Tantalum, Platinum, Iridium or any alloy thereof may beembedded or encapsulated into the coating of the device.

[0074] A further example of yet another manner of fabricating thestent-graft assembly involves wrapping a first tape about the mandrel.Loading the stent onto the mandrel over the first tape. Wrapping asecond tape over the stent. And then applying a hot shoe proximate theinterstices between the stent support members to sinter the two layersof tape together.

[0075] Suitable membrane material also may include autographs, which arevessels transplanted within the patient or host; allografts, which referto vessels transplanted from a donor which is a member of the samespecies as the patient or host; or xenografts, which are transplantedfrom a donor which is not a member of the same species as the patient orhost.

[0076] Further, the instant invention can also be used for indicationsother than repairing and/or providing radial support to a body lumen.Other examples include aneurysm isolation and vessel occlusion. Theforegoing embodiments and examples are illustrative and are in no wayintended to limit the scope of the claims set forth herein.

We claim:
 1. A stent-graft assembly comprising: a generally cylindricalstent comprising at least one support member, an exterior and aninterior, a medial region, a proximal region and a distal region, saidat least one support member defining a passageway through the stent; atleast one membrane, said at least one membrane affixed to at least aportion of at least one of said interior and exterior, wherein the atleast one membrane defines at least one of a luminal surface and avascular surface, said at least one membrane being less than 0.040 inchthick.
 2. The stent-graft assembly according to claim 1 wherein themembrane is less than 0.0016 inch thick.
 3. The stent-graft assemblyaccording to claim 1 wherein the at least one membrane is of generallyuniform thickness.
 4. The stent-graft assembly according to claim 1wherein the stent further comprises: a first polymeric coatingsubstantially encapsulating at least a portion of the at least onesupport member; and the at least one membrane is affixed to the coating.5. The stent-graft assembly according to claim 4 wherein the at leastone membrane is porous and the coating extends into the pores of themembrane.
 6. A stent-graft assembly according to claim 4 wherein the atleast one membrane and the coating are homogeneously bound to oneanother.
 7. The stent-graft assembly according to claim 1 wherein thestent comprises at least one interstice, and the at least one membranecomprises a first inner membrane defining a luminal surface and a secondouter membrane defining a vascular surface, wherein the first and secondmembranes are bound together through the at least one interstice.
 8. Thestent-graft assembly according to claim 7 wherein the at first onemembrane is sintered to the second membrane.
 9. The stent-graft assemblyaccording to claim 1 wherein the assembly also comprises a coating atthe proximal and distal regions of the assembly.
 10. The stent-graftassembly according to claim 9 wherein the coating substantiallyencapsulates the exterior and the interior of the at least one membraneat the proximal and distal regions of the assembly.
 11. The stent-graftassembly of claim 4 wherein the assembly also comprises a second coatingat the proximal and distal regions of the assembly.
 12. The stent-graftassembly of claim 11 wherein the second coating substantiallyencapsulates the exterior and the interior or the at least one membraneat the proximal and distal regions of the assembly.
 13. The stent-graftassembly of claim 1 wherein said at least one membrane is a polymerselected from the group consisting of polyurethane,polytetrafluoroethylene, dimethyl terephthalate, polyester, polyethyleneterephthalate and silicone.
 14. The stent-graft assembly of claim 4wherein the coating is a polymer selected from the group consisting ofpolyurethane, flourinated ethylene propylene and silicone.
 15. The stentgraft assembly of claim 1 wherein the at least one support membercomprises: at least one stent element formed of a plurality ofsubstantially straight segments and configured to provide a plurality ofupper and lower peaks; and the at least one stent element being capableof retaining a compressed configuration while mounted onto an outersurface of a catheter for delivery to an affected area of a vessel untilapplication of an outward radial force to form an expandedconfiguration.
 16. The stent-graft assembly of claim 1 wherein themembrane comprises a primary diameter and wherein the membrane isdistensible over a range of between 7 and 100% beyond the primarydiameter.
 17. A method of forming a stent-graft assembly, the methodcomprising the steps of: preparing at least one tube by first providinga polymeric tape of less than 0.010 inch thickness; winding thepolymeric tape helically around at least a portion of the length of themandrel; placing the wrapped mandrel in an oven at a sufficienttemperature and for a sufficient time to achieve sintering of the tape;providing a generally cylindrical stent having an interior and anexterior, first and second ends and at least one support member; coatingat least a portion of the at least one support member with a coating tosubstantially encapsulate at least a portion of the at least one supportmember; placing the at least one tube contiguous with at least a portionof the interior or the exterior of the stent to define at least one of aluminal surface or a vascular surface; and introducing a solvent inorder to bond the at least one tube to the coating.
 18. The method ofclaim 17 wherein the step of coating the stent comprises: mounting anend of the stent on a rotating mandrel; heating the stent; spraying therotating stent with polymer in solution; curing the stent; alternatingthe end of the stent that is mounted on the mandrel; repeating theforegoing steps.
 19. The method of claim 17 wherein the step of coatingthe stent comprises a vapor deposition process.
 20. The method of claim17 wherein the step of coating the stent comprises dipping the stentinto a polymeric solution.
 21. The method of claim 17 wherein thecoating is a polymer selected from the group consisting of polyurethane,silicone and flourinated ethylene propylene.
 22. The method of claim 17wherein the tape comprises a polymer selected from the group consistingof ePTFE, polyurethane, dimethyl terephthalate, polyester, polyethyleneterephthalate and silicone.
 23. The method of claim 17 wherein thestent-graft assembly also comprises a proximal region and a distalregion, with the additional step of coating the proximal and distalregions of the stent-graft assembly.
 24. The method according to claim17 wherein the tape comprises a width and a plurality of edges, whereinthe tape is wound around the mandrel such that adjacent edges of tapeoverlap 10-60 per cent of the width of the tape.
 25. The methodaccording to claim 17 wherein the tape is wound about the mandrel at anangle to the longitudinal axis of the mandrel, wherein the angle isbetween 30 and 60 degrees.
 26. The method according to claim 17 whereinthe wrapped mandrel is heated in an oven for between 30 and 45 minutes.27. The method according to claim 17 wherein the step of introducing asolvent comprises placing the assembly within a super-saturatedatmosphere of solvent.
 28. A method for preparing a stent-graftassembly, the method comprising the steps of: providing a polymeric tapeof less than 0.010 inch thickness; helically winding the tape about amandrel; heating the wrapped mandrel at sufficient temperature forsufficient time to achieve sintering of the tape to prepare a firstthin-walled polymeric tube; removing the tube from the mandrel;repeating the foregoing steps to prepare a second thin-walled polymerictube; providing a generally cylindrical stent having an interior and anexterior, a proximal region and a distal region, at least one intersticeand at least one support member; lining at least a portion of theinterior of the stent with the first tube to define a luminal surface;placing the second tube over at least a portion of the exterior of thestent to define a vascular surface; and bonding the first and secondtubes to one another through the at least one interstice of the stent.29. The method according to claim 28 with the added step of dipping theproximal and distal regions of the assembly into a polymeric solution.30. The method according to claim 28 wherein the step of bonding thefirst tube to the second tube comprises heating the assembly forsufficient time at sufficient temperature to achieve sintering of thetubes to one another through the at least one interstice.
 31. A methodfor preparing a thin-walled graft tube, the method comprising the stepsof: providing a polymeric tape of less than 0.010 inch thickness;helically winding the tape about a mandrel; applying pressure to thewrapped mandrel; and heating the wrapped mandrel under pressure at asufficient temperature for a sufficient time to achieve sintering of thetape.